Cladistics and "Eclecticism"

[Curtis Clark]

At 08:19 AM 2/5/02, Richard Jensen wrote:
>I didn't say anything went extinct.  What I said was that cladists have
>explained it to me as the taxon (species A) "going extinct" at the species
>level.  As you said, it no longer exists as a "species level" taxon.

I just want to make it clear that as far as I am concerned, Tom is on his
own when it comes to his views of speciation. I understand them, they make
logical sense to me, but I don't find them useful for dealing with the
biological phenomena. Even among the "orthodox", there are differences of
opinion (suggesting that perhaps the epithet "strict cladist" is undeserved
or misapplied).

At 07:18 AM 2/5/02, Pierre Deleporte wrote:
>A problem seems to arise if only one population evolves, and the other
>remains exactly the same in all its characters: should we apply the
>cladistic convention of giving them both terminal taxon status?
>But in the real life, we did not observe the evolution of the populations.
>Then we are facing two different taxa, because they carry different
>character sets.

Questions of classification aside (for the moment), those of us that study
speciation do in fact want to infer that which we cannot observe, and one
good piece of evidence for speciation by peripheral isolation is that the
putative "ancestral" species has no apomorphies that are not also shared by
its derivative. If enough time passes that the ancestral species develops
autapomorphies of its own, then the signal is lost, and ordinary Hennigian
rules are perfectly adequate.

>- conventions for naming taxa in case of a well documented reticulate
>phylogeny: botanists could provide nice real examples here. How should we
>name such things? With markers?

This is a problem only in a subset of cases. Species resulting from
hybridization of closely related parents are often in the same higher taxon
(ordinarily genus) as their parents. At the other extreme, lineages
resulting from putative ancient hybridization are often so obscured by time
that any classificatory treatment is a guess.

It's the situations in the middle that "matter", but even there, the
problem is often avoided. Our bread and pasta wheats are the result of
intergeneric hybridization between Triticum and Aegilops, except that now
most botanists put the Aegilops species in Triticum (not to avoid
"cladistic problems" but rather in an attempt to pay lip service to a
reproductive species concept). Sometimes species of intergeneric hybrid
origin are originally given "hybrid names" that properly belong only to
F1s, and the name sticks (Raphanobrassica comes to mind: the artificial
alloploid between cabbage and radish).

A genus I study, Encelia of the Asteraceae, has two well-defined clades,
and one of the species of hybrid origin has parents from each clade. Were I
to name the clades as subgenera, I would be faced directly with the issue
of where to put the hybrid species.


--
Curtis Clark                  http://www.csupomona.edu/~jcclark/
Biological Sciences Department             Voice: (909) 869-4062
California State Polytechnic University      FAX: (909) 869-4078
Pomona CA 91768-4032  USA                  jcclark at csupomona.edu